U.S. patent number 4,650,951 [Application Number 06/884,884] was granted by the patent office on 1987-03-17 for method of welding laminates each having the structure of metal layer/thermally softenable insulating layer/metal layer.
This patent grant is currently assigned to Mitsui Petrochemical Industries, Ltd.. Invention is credited to Hitoshi Koga, Masushi Nishimoto, Takehisa Noborio.
United States Patent |
4,650,951 |
Koga , et al. |
March 17, 1987 |
Method of welding laminates each having the structure of metal
layer/thermally softenable insulating layer/metal layer
Abstract
A method of resistance-welding two laminates each having a basic
structure of a metal layer/a thermally softenable insulating
layer/a metal layer, which allows welding with excellent welding
strength and good outer appearance of a welded spot. In this
method, two laminates are prepared in which each metal layer has a
thickness of 0.02 to 0.5 mm, and a ratio of the total thickness of
the metal layers of each laminate to the thickness of the laminate
falls within a range between 1/3 and 2/3. Electrodes held at a
temperature above the softening temperature of the insulating
layers are urged against the laminates to soften the insulating
layers and so bring the metal layers into contact with each other
and to resistance-weld the laminates.
Inventors: |
Koga; Hitoshi (Iwakuni,
JP), Noborio; Takehisa (Iwakuni, JP),
Nishimoto; Masushi (Yamaguchi, JP) |
Assignee: |
Mitsui Petrochemical Industries,
Ltd. (Tokyo, JP)
|
Family
ID: |
16013843 |
Appl.
No.: |
06/884,884 |
Filed: |
July 11, 1986 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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654214 |
Sep 25, 1984 |
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Foreign Application Priority Data
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Sep 26, 1983 [JP] |
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58-176446 |
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Current U.S.
Class: |
219/118;
219/91.2 |
Current CPC
Class: |
B23K
11/163 (20130101); H05K 3/361 (20130101); H05K
3/4084 (20130101); H05K 3/328 (20130101); H05K
2203/1572 (20130101); H05K 2201/0129 (20130101); H05K
2203/0195 (20130101); H05K 2203/1189 (20130101) |
Current International
Class: |
B23K
11/16 (20060101); H05K 3/40 (20060101); H05K
3/36 (20060101); H05K 3/32 (20060101); B23K
011/16 () |
Field of
Search: |
;219/91.2,91.21,91.22,91.23,92,93,117.1,118 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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44-18176 |
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Aug 1969 |
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JP |
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106691 |
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Aug 1980 |
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JP |
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187186 |
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Nov 1982 |
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JP |
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Other References
US. patent application Ser. No. 559,239, filed Jun. 21,
1966..
|
Primary Examiner: Goldberg; E. A.
Assistant Examiner: Sigda; C. M.
Attorney, Agent or Firm: Bacon & Thomas
Parent Case Text
This application is a continuation of application Ser. No. 654,214,
filed Sept. 25, 1984, now abandoned.
Claims
What is claimed is:
1. A method of resistance-welding two laminates each having a basic
structure of a metal layer/a thermally softenable insulating
layer/a metal layer, comprising the steps of:
preparing laminates in which the thickness of each metal layer
falls within a range between 0.02 and 0.5 mm and the ratio of the
total thickness of the two metal layers of each laminate to the
total thickness of the laminate falls within a range between 1/3
and 2/3;
holding a pair of electrodes for resistance-welding on opposite
sides of overlapped portions of the two laminates, heating the
overlapped portions to a temperature not lower than the softening
temperature of the insulating layers by electrodes which are heated
by heaters arranged around the electrodes to a temperature higher
than the softening temperature of the insulating layers, thus
softening the insulating layers, and applying pressure to the pair
of electrodes at the overlapped portions to thereby bring the metal
layers of the two laminates into contact with each other; and
supplying power to said pair of electrodes while said metal layers
of the two laminates are in contact with each other.
2. A method according to claim 1, wherein heaters for heating the
electrodes are arranged around the electrodes.
3. A method according to claim 1, wherein a holding jig in contact
with the laminates surrounds one of said electrodes, the surface of
said holding jig is parallel to the tip of said electrode, contact
areas of said holding jig with the laminates being wider than a
thermally deformed area of the welded spot of the laminates.
4. A method according to claim 1, wherein the thermally softenable
insulating layers consist of a thermoplastic resin.
5. A method according to claim 4, wherein the thermoplastic resin
is a polyolefin.
6. A method according to claim 1, wherein the metal layers consist
of a material selected from the group consisting of a metal, an
alloy and a metal member and an alloy member surface-treated with a
conductive material.
7. A method according to claim 1, wherein the resistance welding is
spot welding.
8. A method according to claim 1, wherein the metal layers of the
laminates consist of a material selected from the group consisting
of iron and iron-based alloys, each of said electrodes having at
least tips thereof consisting of molybdenum.
9. A method according to claim 1, wherein when the insulating
layers consist of a polypropylene, the electrodes are heated to a
temperature falling within a range between 260.degree. and
300.degree. C.
10. A method according to claim 3, wherein when the insulating
layers consist of a polypropylene, the electrodes having the
holding jig therearound are heated to a temperature falling within
a range between 240.degree. and 300.degree. C.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of resistance-welding
laminates each having a basic three-layered structure consisting of
metal layer/thermally softenable insulating layer/metal layer
2. Description of the Prior Art
Laminated materials obtained by combining a metallic material with
various nonmetallic materials to improve various properties of the
metallic material have been proposed. Examples of such laminated
materials include a laminated material in which a synthetic resin
film is formed, or is coated, on the surface of a metallic material
so as to prevent corrosion of the metal; a laminated material for
vibration prevention in which a thin layer of a vibration absorbing
material such as rubber is formed inside a metallic material so as
to provide good vibration prevention; and a light-weight laminated
material consisting of an inner layer of a synthetic resin and a
thin outer layer of a metal so as to provide a light-weight
material with flexural stiffness equivalent to a metallic material.
U.S. Pat. No. 4,313,996 (Feb. 2, 1982) discloses an example of a
light-weight laminated material having a structure of
metal/synthetic resin/metal. A structure having the following
dimensions is disclosed: each metal skin layer is from about 2 to
20 mils (0.05-0.5 mm) thick, the ratio of the core thickness to
skin thickness is less than 9:1, and the total laminate thickness
is from about 5 to about 65 mils (0.13-1.65 mm). However, this
reference does not describe the welding method.
The laminated metallic materials described above are all combined
with electrically insulating materials such as synthetic resins.
Therefore, two such laminated metallic materials cannot be welded
by a conventional welding method since the overall structure is not
conductive and so cannot be welded together.
In view of this, various improved welding methods have been
proposed and actually practiced. FIG. 1 shows a welding method for
projection welding laminates each having a metal/insulating
material/metal structure. In this method, one laminate 1 consists
of an internal insulating layer 4 sandwiched between metal layers
3a and 3b. Another laminate 2 consists of an internal insulating
layer 6 sandwiched between metal layers 5a and 5b. These laminates
1 and 2 are to be welded together. Projection welding is performed
such that electrodes 7 and 8 are brought into contact with the
opposing metal layers 3b and 5a, and holding jigs 20a and 20b hold
the upper and lower metal layers 3a and 5b. However, in a laminated
metallic material obtained in this manner, only the metal layers 3b
and 5a are welded. Metal layers 3a and 5b are not welded.
Therefore, the welding strength is very weak. If the metal layer is
a thin layer, the welded portion cannot serve a practical
purpose.
FIG. 2 shows a known welding method utilizing a bypass circuit.
According to this method, each of two laminates 9 and 10 to be
welded has the following structure. The laminate 9 has an internal
insulating layer 12 sandwiched between metal layers 11a and 11b.
The laminate 10 consists of an internal insulating layer 14
sandwiched between metal layers 13a and 13b. A bypass circuit 15 is
formed between the metal layers 11a and 13b. In the welding start
period, a current flows through an electrode 16, the metal layer
11a, the bypass circuit 15, the metal layer 13b, and an electrode
17. Then, Joule heat is generated in the metal layers 11a and 13b
and melts the internal insulating layers 12 and 14. According to
this method, the melted portion of the insulating layers 12 and 14
near the electrode is made to flow transversely by the urging force
of the electrodes 16 and 17. At the same time, the metal layers 11a
and 13b are deformed and urged against the metal layers 11 b and
13a. As a result, a current flows directly between the electrodes
16 and 17 and the metal layers 11a, 11b, 13a and 13b to allow
welding of the laminates. This method achieves excellent welding
when applied to light-weight laminated materials in which the outer
metal layers are thick and the internal insulating layers are thin.
However, when this method is applied to a light-weight laminated
material in which the outer metal layers are thin and the inner
insulating layers are thick, problems are encountered. A
light-weight laminated material of this type which can be welded by
the method of the present invention is rendered light-weight by
substituting the inner layer with a light material (normally
insulating material) without decreasing the flexural stiffness.
Such a light-weight laminated material is intended for use in a
casing or the like. Therefore, deformation of the laminate at
points other than the welding spot cannot be neglected.
Furthermore, in a light-weight laminate of this type, since the
metal layer is thin, the outer metal layer is significantly damaged
due to recessed deformation upon welding. Since the internal
insulating layer generally consists of an organic material, it is
decomposed and generates a gas at a melting point of the metal upon
welding. This gas cannot diffuse out of the insulating layer due to
the metal layers covering the insulating layer. The trapped gas
then causes the problem of "doming". This tendency becomes
particularly notable when the insulating layer is thick. However,
when the method shown in FIG. 2 is adopted, the area in which the
internal resin layer melts is not confined to the vicinity of the
electrodes but also extends to the area connecting the electrodes
and the bypass circuit. Therefore, the amount of resin which is
squeezed by the urging forces of the electrodes is undesirably
increased. In addition, a large amount of decomposition gas is
produced. The laminate is distorted or waved within a wide area
having the welded portion as its center. A good weld cannot,
therefore, be obtained. In the method shown in FIG. 2, every time
the welding spot is changed, the position of the bypass circuit
must be changed and adjusted. This involves complex procedures.
Furthermore, the shape of laminated materials which may be welded
is limited due to the apparatus.
U.S. patent application Ser. No. 559,239 (June 21, 1966) discloses
a method of welding conductors which are not coated with an
insulator to a lead wire which is coated with an insulator.
External heaters are connected to the electrodes to soften the
insulators on the lead wire. Thus, the conductors and the lead wire
are forcibly brought into contact with each other and are welded
together. In this method, one part to be welded is the insulated
wire, and the others are conductors which are not coated with an
insulator. In such a welded article, the decomposition gas produced
by heating the insulating material is freely discharged outside the
article, so that a problem of "doming" is avoided.
U.S. Pat. No. 3,155,809 (Nov. 3, 1964) discloses a spot-welding or
resistance-welding method. According to this method, when
conductors coated with an insulator, particularly flexible
ribbon-type cables, are electrically coupled, a pair of heated
electrodes is used to clamp the conductors so as to soften the
insulators. Then, the metal portions are physically brought into
contact with each other. A welding current is made to flow between
the electrodes to allow spot welding or resistance-welding.
According to this method, as in the method disclosed in U.S. patent
application Ser. No. 559,239, members to be welded are insulator
coated conductors. With such members, the decomposition gas
produced upon heating the insulators is freely discharged outside
the structure, so that there is no doming problem.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a
resistance-welding method, in which laminates each having a
structure of metal/thermally softenable insulating material/metal
are resistance-welded in such a manner that doming due to gas
formation in the insulating material is prevented such that the
reproducibility of the process and welding strength are improved
and deformation of laminates at points other than the welded spots
is prevented, thereby providing a welded structure having an
excellent outer appearance.
In order to achieve the above object of the present invention,
there is provided a resistance-welding method comprising the steps
of:
preparing two laminates in which each metal layer has a thickness
of 0.02 to 0.5 mm, and the total thickness of the metal layers is
1/3 to 2/3 of the total thickness of the laminate;
holding a pair of electrodes for resistance-welding an overlapped
portion of the laminates at a temperature higher than a softening
temperature of insulating layers, and urging said electrodes
against surfaces at a welding spot of the laminates to soften the
insulating layers, thereby contacting every adjacent metal layer;
and
supplying power to the pair of electrodes while all the adjacent
metal layers are in contact with each other, thereby
resitance-welding the laminates.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view showing a conventional method of
resistance-welding laminates employing projection welding;
FIG. 2 is a schematic view showing a conventional method of
resistance-welding laminates utilizing a bypass circuit;
FIG. 3 is a schematic view showing a method of resistance-welding
laminates according to an embodiment of the present invention;
FIG. 4 is a sectional view of laminates welded by the method shown
in FIG. 3;
FIG. 5 is a schematic view showing a method of resistance-welding
laminates according to another embodiment of the present invention;
and
FIG. 6 is a sectional view showing laminates welded by the method
shown in FIG. 5.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The resistance-welding method of the present invention is adapted
to weld two laminates each having a basic structue of metal
layer/thermally softenable insulating layer/metal layer. A laminate
to be welded by the method of the present invention is intended for
use in a casing or the like and is a light-weight substitute for a
metal plate. In this laminate, the inner layer of a metal plate is
replaced with a light-weight insulating layer, so that the overall
laminate can be rendered light without degrading its flexural
stiffness.
Each metal layer of such a laminate may consist of a metal such as
iron, lead, zinc, or aluminum; an alloy thereof with other elements
such as carbon, chromium, or titanium; or such metals or alloys
with various conductive surface-treated layers formed by metal
plating or chemical treatment. Each metal layer is selected to have
a thickness of 0.02 to 0.5 mm. The ratio of the total thickness of
the two metal layers of each laminate is 1/3 to 2/3 of the total
thickness of the laminate. In order not to degrade the flexural
stiffness, each metal layer must have a certain thickness. However,
to provide a light laminate, each metal layer should be as thin as
possible. If each metal layer is thin, the insulating layer must be
thick to keep thickness of the laminate uncharged. The thicker the
insulating layer, the more gas it generates upon welding. In this
case, the thin metal layer may not be able to withstand the
pressure of the gas and deforms. Therefore, the welded spot may
have an unsatisfactory strength and a poor outer appearance and be
easily deformed. In view of this, each metal layer must have a
thickness above a predetermined thickness. However, if a metal
layer is too thick, when the insulating layer is heated through the
metal layers, the heat is dissipated by the metal layers to a great
extent, resulting in a long welding time. Therefore, each metal
layer must have a thickness less than a predetermined value.
The absolute and relative thickness of each metal layer must thus
be defined to fall within predetermined ranges in order to maintain
the properties of the laminates, to perform satisfactory welding,
and to improve the strength and outer appearance of the welded
spot. The specific ranges were determined by the present inventors
in experiments under different conditions and will be described
with reference to Example 4. Although U.S. Pat. No. 4,313,996
specifies the dimensions of the metal layers and insulating
(synthetic resin) layers having the same structure as that of the
present invention, they were not determined for the purpose of
performing satisfactory resistance-welding and providing
satisfactory strength and outer appearance at the welded spot.
The material of the thermally softenable insulating layer contained
in each laminate can be a thermoplastic resin such as a polyolefin,
polyvinyl chloride, polyvinylidene chloride, polyester, polyamide,
polycarbonate, polyvinyl acetate, polyacetal, polystyrene, ABS
resin, methyl polymethacrylate, or a fluorine-containing resin. Of
these materials, preferred examples in view of formability and
weldability may include polyolefins such as homopolymers or
copolymers of an .alpha.-olefin, e.g., ethylene, propylene,
1-butene, 1-pentene, 3-methyl-1-butene, 1-hexene,
4-methyl-1-pentene, 1-heptene, or 1-octene; copolymers of these
.alpha.-olefins with small amounts of monomers, e.g., vinyl
acetate, acrylic acid, methacrylic acid, methyl acrylate, or methyl
methacrylate; or graft-modified polyolefins obtained by grafting
the above polyolefins with monomers such as vinyl acetate, acrylic
acid, methacrylic acid, maleic acid, fumaric acid, methyl acrylate,
ethyl acrylate, ethyl maleate, or maleic anhydride. The material of
the thermally softenable insulating layer may be a rubbery material
such as natural rubber, a butadiene-styrene copolymer, nitrile
rubber, chloroprene rubber, polyisoprene, butyl rubber, or
polyisobutylene. Instead of these materials, the thermally
softenable insulating layer may consist of other insulators which
can be softened and made to flow upon being heated.
The insulating layer and the metal layer can be laminated by
conventional methods. For example, the insulating layer can be
melted and adhered to the metal layer. Alternatively, the
insulating layer and the metal layer can be adhered together with
an adhesive.
The method of resistance-welding two laminates each having the
above-mentioned structure will be described with reference to the
embodiment shown in FIG. 3.
One laminate 21 has an internal thermally softenable insulating
layer 22 and metal layers 23a and 23b sandwiching it. Another
laminate 24 has an internal thermally softenable insulating layer
25 and metal layers 26a and 26b sandwiching it. The overlapping
portion of these laminates 21 and 24 forms a welding spot.
Electrodes 27 and 28 are arranged at the two surfaces of the
welding spot. Heaters 29 and 30 are arranged around the electrodes
27 and 28, respectively. The heaters 29 and 30 heat the electrodes
27 and 28 and keep them at a temperature higher than the softening
temperature of the insulating layers 22 and 25. When the insulating
layers consist of polypropylene, the electrodes 27 and 28 are kept
at a temperature higher than the softening temperature of
polypropylene, i.e., 165.degree. C. The heated electrodes 27 and 28
are brought into contact with the laminates 21 and 24. Then, inside
the respective laminates, heat from the electrodes 27 and 28 is
conducted from the metal layers 23a and 26b to the insulating
layers 22 and 25, and the insulating layers 22 and 25 are
sequentially fluidized. The fluidized portions of the insulating
layers mainly overlap the portions immediately below the metal
layers since the electrodes are in point contact or in surface
contact close to point contact with the metal layers. As a result,
the electrodes urged against the laminates squeeze the fluidized
portions of the insulating layers and come closer to each other.
The insulating layers are further squeezed out at the fluidized
portions, and the metal layers 23a and 25b are deformed, so that
the metal layers 23a, 23b, 26a and 26b are brought into contact
with each other. The squeezed portions of the insulating layers
bulge around the welding spot and are cooled and solidified.
Another method for softening and fluidizing the insulating layers
may be adopted wherein heated punches or the like are pressed
toward a prospective welding spot of laminates to fluidize the
insulating layers, the fluidized insulating layers are squeezed by
the pressure of the punches, and electrodes are then brought into
contact with the welding spot. However, this method is not suitable
for welding laminates according to the present invention for the
following reason. When the heated punches are removed and the
electrodes are brought into contact with the metal layers, the
deformed metal layers spring back and are separated from each other
so the insulator flows into the space formed between the separated
metal layers. Then, power cannot be supplied to the metal layers.
Furthermore, due to the two-step stress exerted by the heated
punches and electrodes, a thin matal layer may be torn away.
According to the method of the present invention, before or when
the metal layers 23a, 23b, 26a and 26b are brought into direct
contact with each other, a current is supplied to the electrodes 27
and 28 to resistance-weld the laminates 21 and 24. As a result, as
shown in FIG. 4, a uniformly bulged insulating layer is formed to
surround a directly welded spot 31. The welded spot has a high
welding strength and a good outer appearance. The inventors think
that this is attributed to the following reason. According to the
present invention, since both the electrodes 27 and 28 are heated,
the insulating layers are softened within a short time to prevent
the generation of a decomposition gas from the insulating layers.
Generation of the decomposition gas is further prevented by using
laminates 21 and 24 having insulating layers of a small thickness.
Therefore, since welding can be performed without adverse influence
from a decomposition gas, reproducibility of the welding process
and the welding strength are improved, doming is prevented, and a
good outer appearance is obtained.
Electrodes 27 and 28 may be made of a material ordinarily used in
resistance welding and, preferably, one of the materials described
hereinafter.
The material is generally one having an electric resistance lower
than that of the material to be welded. When the material to be
welded is, for example, iron, an alloy such as a copper-based
chromium alloy is used so as to suppress heat generation due to
contact resistance between the electrodes and the material to be
welded and to prevent fusing. However, since laminates of the
present invention have insulating layers between metal layers, the
contact resistance between the metal layers upon welding is
unstable. Even if the tip shape of the electrode is slightly
changed, the contact resistance is significantly influenced and the
welded area becomes unstable. For this reason, with conventional
copper-based chromium alloy electrodes, dressing of electrode tips
is performed after welding 30 spots to assure satisfactory welding
performance. According to the present invention, although
electrodes of this alloy can be used, if metal layers consist of
iron or an iron alloy, at least the tips of the electrodes can be
made of molybdenum having a resistance equivalent to that of iron.
When electrodes of such materials are used, the electrodes generate
heat upon being powered so as to facilitate melting of insulators
utilizing the contact resistance at the interface between the metal
layers. For this reason, the above described problem can be
eliminated, and the dressing interval of electrodes can be extended
to welding 300 or more spots.
When molybdenum electrodes are used to resistance-weld iron
members, the electrodes and iron fuse and the iron members cannot
be welded. However, with laminates having a structure of iron
layer/insulating layer/iron layer, the contact resistance at the
interface is high. Thus, the contact resistance between iron and
molybdenum is considered to be suppressed, and consequently, fusing
of the electrodes is prevented.
When molybdenum electrodes are used, series-welding can be
performed. When series-welding of laminates according to the
present invention is performed, using electrodes made of
copper-based chromium alloy, the contact resistance inside the
laminates is inevitably unstable. Consequently, the welding
strength is too great at one spot while it is too small at another
spot, thus preventing welding. However, with molybdenum electrodes
heating by the contact resistance can be negated by the heat
generated by the electrodes, and uneven welding strength can be
avoided. Series-welding is thus facilitated.
FIG. 5 shows another embodiment of a welding method according to
the present invention. An object of this emodiment is to eliminate
deformation of one surface of the welded spot so as to provide a
smooth welded spot when viewed from one side. In order to achieve
this object, a holding jig 40 is provided around an electrode 28 on
the same side of a welding spot on which a smooth surface is to be
formed. The holding jig 40 must be arranged parallel to the tip of
the electrode 28, have a smooth surface in contact with a laminate
24 and have an area wider than the thermally deformed area of the
welded portion. The material of the electrode 28 at the side of the
holding jig 40 preferably has a greater hardness than that of the
electrode 27 at the other side in order to prolong the electrode
life. As in the case of the electrode 28, the holding jig 40 is
heated to and kept at a temperature higher than the softening
temperature of insulating layers so as to improve the welding speed
and the appearance of the welded spots. When welding is performed
using the holding jig 40, even if the insulating layers are heated
and softened, the metal layer 26b in contact with the holding jig
40 is not deformed and is kept smooth, as shown in FIG. 6.
Therefore, the welded spot of the finished, welded laminates have
one smooth side and a very good outer appearance. In order to
provide the same effect, a back bar electrode can be used in place
of the holding jig.
The embodiments shown in FIGS. 3 to 6 are described with reference
to spot-welding. However, the present invention can also be applied
to seam-welding or projection-welding.
The present invention will now be described by way of its
Examples.
EXAMPLE 1
Resistance-welding of laminates was performed by the method shown
in FIGS. 3 and 5. The welding results together with the materials,
dimensions and welding conditions are shown in Table 1. Two metal
plates and insulating layers of laminates were adhered with a
modified polyolefin adhesive layer having an adhesive functional
group.
TABLE 1
__________________________________________________________________________
Welding condition Ther- mally Laminate Upper Lower de- Con-* First
metal Second metal Insulating electrode electrode formed tact layer
layer layer Tem- Tem- area area Weld- Thick- Thick- Thick- pera-
pera- (diam- (diam- ing Eval- Meth- Mate- ness Mate- ness Mate-
ness ture Mate- ture Mate- eter eter re- ua- No. od rial (mm) rial
(mm) rial (mm) (.degree.C.) rial (.degree.C.) rial in mm) in mm)
sult tion
__________________________________________________________________________
1 FIG. 3 iron 0.2 iron 0.2 poly- 0.42 280 Cu--Cr 280 Cu--Cr 10 4
uni- o foil foil pro- form pyl- pro- ene jec- tion 2 FIG. 5 iron
0.2 iron 0.2 poly- 0.42 300 Cu--Cr 240 Cu--Cr 12 35 one o foil foil
pro- smooth pyl- side ene
__________________________________________________________________________
o . . . Very good outer appearance (Primary welding voltage: 160 V;
power cycle number: 5 c/s; electrode pressure: 400 kg) *The contact
area between the holding jig and the laminates
EXAMPLE 2
Various welding conditions were set wherein the heating temperature
of the electrodes and the softening temperature of the insulating
layers were varied, and laminates were welded by the method shown
in FIG. 3.
The obtained results are shown in Table 2 together with the
structure of the laminates and the welding conditions. A welder
used in Example 2 was an AC spot welder 3111-3, available from
Durex Co., Ltd., West Germany, connected to a power source control
apparatus A-11, available from the same company. In order to allow
a variable voltage to be applied to the primary side of the welding
transformer, variable-voltage transformers of 200 V and 20 A were
added. Upper and lower welding electrodes (of 12 mm diameter) of
the welder had truncated conical shapes having a top diameter of 4
mm and a cone angle of 60.degree.. Ring heaters of 600 W capacity
having temperature controllers were mounted on these
electrodes.
TABLE 2
__________________________________________________________________________
Laminate Welding condition First metal layer Second metal layer
Insulating layer Upper electrode Thickness Thickness Thickness
Temperature No. Method Material (mm) Material (mm) Material (mm)
(.degree.C.) Material
__________________________________________________________________________
3 FIG. 3 steel* 0.2 steel* 0.2 polypropylene 0.42 25 Cu--Cr plate
plate 4 FIG. 3 steel* 0.2 steel* 0.2 polypropylene 0.42 220 Cu--Cr
plate plate 5 FIG. 3 steel* 0.2 steel* 0.2 polypropylene 0.42 240
Cu--Cr plate plate 6 FIG. 3 steel* 0.2 steel* 0.2 polypropylene
0.42 260 Cu--Cr plate plate 7 FIG. 3 steel* 0.2 steel* 0.2
polypropylene 0.42 280 Cu--Cr plate plate 8 FIG. 3 steel* 0.2
steel* 0.2 polypropylene 0.42 300 Cu--Cr plate plate 9 FIG. 3
steel* 0.2 steel* 0.2 polypropylene 0.42 300 Cu--Cr plate plate 10
FIG. 3 steel* 0.2 steel* 0.2 polypropylene 0.42 300 Cu--Cr plate
plate 11 FIG. 3 steel* 0.2 steel* 0.2 polypropylene 0.42 300 Cu--Cr
plate plate 12 FIG. 3 steel* 0.2 steel* 0.2 polypropylene 0.42 300
Cu--Cr plate plate 13 FIG. 3 steel* 0.2 steel* 0.2 polypropylene
0.42 300 Cu--Cr plate plate
__________________________________________________________________________
Welding condition Welding result Thermally Time deformed Contact
before Lower electrode area area current Welding Temperature
(diameter (diameter flow pressure No. Method (.degree.C.) Material
in mm) in mm) (second) (kg/spot) Evaluation Remarks
__________________________________________________________________________
3 FIG. 3 25 Cu--Cr -- 4 60 or -- x No current more flow 4 FIG. 3
220 Cu--Cr -- 4 60 or -- x 1 minute or more more before current
flow 5 FIG. 3 240 Cu--Cr 12 4 20 80 .DELTA. Doming around welded
spot 6 FIG. 3 260 Cu--Cr 10 4 6 112 o Excellent 7 FIG. 3 280 Cu--Cr
10 4 1> 122 o Excellent 8 FIG. 3 300 Cu--Cr 10 4 1> 140 o
Excellent 9 FIG. 3 240 Cu--Cr 10 4 1 -- .DELTA. Doming around lower
welded spot side 10 FIG. 3 200 Cu--Cr 10 4 3 -- .DELTA. Doming
around lower welded spot side 11 FIG. 3 150 Cu--Cr 10 4 3 --
.DELTA. Doning around lower welded spot side 12 FIG. 3 100 Cu--Cr
-- 4 60 or -- x 1 minute or more before current flow 13 FIG. 3 25
Cu--Cr -- 4 60 or -- x 1 minute or more more before current
__________________________________________________________________________
flow *Electrolytically chromiumtreated plate of soft cold rolled
steel (Tin free steel) o . . . Very good outer appearance .DELTA. .
. . Doming caused by gasification of the contained resin upon
welding x . . . Not practically usable (Primary welding voltage:
160 V; power cycle number: 5 c/s; electrode pressure: 400 kg)
In Example 2, when the upper and lower electrodes were not heated
(sample No. 3), a welding current did not flow. For this reason, a
short-circuit, as shown in FIG. 2, was added. However, thermal
deformation at the welded point was significant and thermal
deformation also occurred in an area between the welded point and
the short-circuit of the current. Thus, the only welded laminates
obtained were those not suitable for practical use. For sample Nos.
4, 12 and 13 (temperature: 220.degree. C. or 300.degree. C.), the
time before current flow after application of pressure on the
electrodes was 1 minute or more. This is not practical from the
viewpoint of work speed. For sample Nos. 5 and 9 to 11
(temperature: 240.degree. C.), heating of the inner resin layer at
the welding point and squeezing of the melted resin were
insufficient. Due to the high temperature applied during welding,
the insulating layer at the welding point is gasified to urge
upward the metal layer around the welded point, thereby causing
doming, which is not desirable from the viewpoints of outer
appearance and welding strength. For sample Nos. 6 to 8
(temperature of 260.degree. C. or higher), an excellent welding
operation could be performed. However, if the electrode temperature
is too high, wear of the electrode tips is significant. Therefore,
the electrode temperature preferably falls within the range of
260.degree. to 300.degree. C.
EXAMPLE 3
Laminates and welder as used in Example 2 were used for welding by
the method shown in FIG. 5. Welding was performed by restricting
the contact area between the holding jig and the laminates to
portions directly above and below the thermally deformed area. The
obtained results are shown in Table 3 below, together with the
structure of the laminates and the welding conditions.
TABLE 3
__________________________________________________________________________
Laminate Welding condition First metal layer Second metal layer
Insulating layer Upper electrode Thickness Thickness Thickness
Temperature No. Method Material (mm) Material (mm) Material (mm)
(.degree.C.) Material
__________________________________________________________________________
14 FIG. 5 steel* 0.2 steel* 0.2 polypropylene 0.42 300 Cu--Cr plate
plate 15 FIG. 5 steel* 0.2 steel* 0.2 polypropylene 0.42 300 Cu--Cr
plate plate 16 FIG. 5 steel* 0.2 steel* 0.2 polypropylene 0.42 300
Cu--Cr plate plate 17 FIG. 5 steel* 0.2 steel* 0.2 polypropylene
0.42 300 Cu--Cr plate plate 18 FIG. 5 steel* 0.2 steel* 0.2
polypropylene 0.42 300 Cu--Cr plate plate 19 FIG. 5 steel* 0.2
steel* 0.2 polypropylene 0.42 300 Cu--Cr plate plate 20 FIG. 5
steel* 0.2 steel* 0.2 polypropylene 0.42 300 Cu--Cr plate plate 21
FIG. 5 steel* 0.2 steel* 0.2 polypropylene 0.42 300 Cu--Cr plate
plate 22 FIG. 5 steel* 0.2 steel* 0.2 polypropylene 0.42 300 Cu--Cr
plate plate 23 FIG. 5 steel* 0.2 steel* 0.2 polypropylene 0.42 300
Cu--Cr plate plate 24 FIG. 5 steel* 0.2 steel* 0.2 polypropylene
0.42 300 Cu--Cr plate plate
__________________________________________________________________________
Welding result Welding condition Time Thermally Contact before
Lower electrode deformed area current Welding Temperature area
(diameter flow pressure No. Method (.degree.C.) Material (diameter
in mm) (second) (kg/spot) Evaluation Remarks
__________________________________________________________________________
14 FIG. 5 300 Cu--Cr 14 12 1> 140 o Rough lower surface 15 FIG.
5 240 Cu--Cr 14 12 1> 138 o Rough lower surface 16 FIG. 5 200
Cu--Cr 14 12 3 -- .DELTA. Rough lower surface 17 FIG. 5 150 Cu--Cr
14 12 6 -- .DELTA. Rough lower surface 18 FIG. 5 100 Cu--Cr -- 12
60 or -- x more 19 FIG. 5 25 Cu--Cr -- 12 60 or -- x more 20 FIG. 5
300 Cu--Cr 14 35 1> 140 o Smooth lower surface 21 FIG. 5 260
Cu--Cr 14 35 1> 140 o Smooth lower surface 22 FIG. 5 240 Cu--Cr
14 35 1> 132 o Smooth lower surface 23 FIG. 5 220 Cu--Cr 14 35
1> 130 .DELTA. Smooth lower surface 24 FIG. 5 150 Cu--Cr 14 35 3
-- .DELTA. Smooth lower surface
__________________________________________________________________________
*Electrolytically chromiumtreated plate of soft cold rolled steel
(Tin free steel) o . . . Very good outer appearance .DELTA. . . .
Doming caused by gasification of the contained resin upon welding x
. . . Not practically usable (Primary welding voltage: 160 V; power
cycle number: 5 c/s; elctrode pressure: 400 kg)
In Example 3, the welding performance was influenced by the
temperature of the upper and lower electrodes, as in the case of
Example 2. Among laminates in which the contact area with the
holding jig is smaller than the thermally deformed area, those
which resulted in satisfactory welding (sample Nos. 14 to 17)
caused ring-like thermal deformation in the lower surface of the
welded point and could not provide one smooth side. Those which had
a contact area with the holding jig larger than the thermally
deformed area had a wider suitable electrode temperature range (for
the lower electrode) of 240.degree. to 300.degree. C., shifted
toward lower temperatures than those in Example 2. Substantially no
thermal deformation was observed around the lower surface of the
welded spot welded within this temperature range, and one smooth
side was provided.
EXAMPLE 4
Welding was performed following the same procedures as those in
Example 1 for laminates in which the thickness of each metal layer
of each laminate and the ratio of the total thickness of the two
metal layers of each laminate to the thickness of the laminate fell
inside and outside the ranges defined according to the present
invention. The obtained results are shown in Table 4 together with
the structure of the laminates and the welding conditions.
TABLE 4
__________________________________________________________________________
Laminate Welding condition First metal layer Second metal layer
Insulating layer Upper electrode Thickness Thickness Thickness
Temperature No. Method Material (mm) Material (mm) Material (mm)
(.degree.C.) Material
__________________________________________________________________________
25 FIG. 3 iron 0.2 iron 0.2 polypropylene 0.42 280 Cu--Cr foil foil
26 FIG. 3 iron 0.2 iron 0.2 polypropylene 1.0 280 Cu--Cr foil foil
27 FIG. 3 iron 0.8 iron 0.8 polypropylene 1.6 280 Cu--Cr foil foil
__________________________________________________________________________
Welding results Welding condition Time Thermally Contact before
Lower electrode deformed area current Welding Temperature area
(diameter flow pressure No. Method (.degree.C.) Material (diameter)
in mm) (second) (kg/spot) Evaluation Remarks
__________________________________________________________________________
25 FIG. 3 280 Cu--Cr 10 4 1> 122 o 26 FIG. 3 280 Cu--Cr 10 4 6
-- x Surface metal layer broke down 27 FIG. 3 280 Cu--Cr 10 4 60 or
-- x 1 minute or more more before current
__________________________________________________________________________
flow o . . . Very good outer appearance .DELTA. . . . Doming caused
by gasification of the contained resin upon welding x . . . Not
practically usable
In Example 4, with a sample (No. 25) in which the thickness of the
metal layer and the ratio of the total thickness of the metal
layers to the thickness of the laminate fell within the ranges
defined by the present invention, an excellent welding performance
was obtained. However, with a sample (No. 26) having thicker
insulating layers because of a smaller ratio of total thickness of
the metal layers compared to the thickness of the laminate, and
with a sample (No. 27) having thicker metal layers, no satisfactory
results were obtained.
* * * * *